The subject invention relates to the production of sintered hard metal bodies adapted for use in cutting tools that are utilized in highly abrasive applications such as metal cutting and rock drilling. More specifically, the subject invention provides for a new and improved multi-layered hard metal body with improved adhesion between the layers.
In the prior art, a variety of hard metal bodies consisting essentially of cemented carbide materials have been utilized in the formation of cutting tools and cutting inserts. In many applications, it is desirable to provide the cutting tool with an outer coating of a highly wear resistant compound to increase the abrasion resistance of the tool. For example, known cutting tools formed from cemented carbide materials have been provided with an outer layer of titanium boride for increasing wear resistance. The resultant increase in abrasion resistance of the cutting tool is in part a function of the adhesion developed between the substrate and the outer wear resistant coating. Accordingly, it is desirable to maximize the adhesion between the substrate and the wear resistant coating material in order to maximize the abrasion resistance of the tool.
In the prior art, various methods have been used in order to increase the adhesion between the substrate and the wear resistant outer coating. One approach is described in T. E. Hale and R. C. Lueth, U.S. Pat. No. 4,268,582, assigned to the same assignee as the subject invention, which relates to the coating of a wear resistant titanium boride layer over a cemented carbide substrate formed from a combination of tungsten carbide and cobalt. In the latter method, silicon, aluminum or boron is initially diffused into the uncoated substrate. An intermediate layer, having a thickness less than 10 microns is then deposited on the treated substrate. The intermediate layer is formed from a combination of titanium carbide and titanium nitride. Thereafter, a thicker layer, of approximately 5 to 20 microns in depth, of the wear resistant titanium boride is deposited over the intermediate layer. While the above disclosed prior art method produced a hard metal body having improved adhesion between the layers, it would be desirable to provide a new and improved hard metal body with even greater resistance to abrasion.
Accordingly, it is an object of the subject invention to provide a new and improved multi-layered hard metal body adapted for use with cutting tools having improved adhesion between the layers.
It is another object of the subject invention to provide a new and improved hard metal body for cutting tools wherein a bonding layer formed from elemental boron is interposed between the substrate and the outer wear resistant coating to increase adhesion between the layers and improve the abrasion resistance of the tool.
It is a further object of the subject invention to provide a new and improved multi-layered hard metal body for use in cutting tools wherein an additional intermediate layer is disposed between the substrate and the boron bonding layer for further enhancing the abrasion resistance of the tool.